1. Field of the Invention
The present disclosure relates to capacitors for liquid crystal display and, more particularly, to a storage capacitor for a multi-domain vertically aligned liquid crystal display.
2. Description of the Related Art
Liquid crystal display (LCD) mainly comprises a liquid crystal display cell having two glass substrates oppositely positioned and a liquid crystal layer interposed therebetween. Vertically-aligned (VA) LCD is a mode using a liquid crystal material having a negative dielectric anisotropy and vertical alignment films. When no voltage is applied, liquid crystal molecules are aligned in a vertical direction and a black display appears. When a predetermined voltage is applied, the liquid crystal molecules are aligned in a horizontal direction and a white display appears. Compared to the twisted nematic (TN) LCD, the vertically-aligned (VA) LCD provides higher contrast, higher response speed, and excellent viewing angle.
However, the VA LCDs still suffer from the problems of decreased contrast ratio and contrast reversal when viewed in a direction not perpendicular to the display area. As a result of the interaction between light and the liquid crystal molecules, light passing through the cell in a vertical incident angle interact with the liquid crystal molecules in a way different from light passing through the cell in a non-vertical incident angle. The contrast ratio between a light transmissive state (white) and a non-transmissive state (black) decreases drastically at an angle not perpendicular to the display, thereby making it less desirable in many applications, such as flat panel television screens and large computer screens.
It is known that viewing angle performance of a VA LCD can be improved by setting the orientation of the liquid crystal molecules inside pixels to a plurality of mutually different directions. European Patent Publication Number 0884626-A2 discloses a multi-domain VA LCD having domain regulating means for regulating the orientation of a liquid crystal in which liquid crystal molecules are aligned obliquely when a voltage is applied so that the orientation will include a plurality of directions within each pixel region.
Typically, the VA LCD described above is a thin film transistor (TFT) LCD mainly comprising a color filter (CF) substrate and a TFT substrate. The CF substrate is typically provided with a plurality of color filters and a common electrode. The TFT substrate is typically provided with a plurality of gate lines formed in parallel to one another, a plurality of data lines, vertically to the gate lines, formed in parallel to one another, and TFTs and pixel electrodes. Usually, spacers are formed between the substrates for defining the gap between the substrates.
The LCD described above is typically provided with a storage capacitor (Cs) to maintain voltage at the pixel electrode within specified limits for a predetermined amount of time after the TFT has been turned off. The storage capacitor is formed of an opaque metal, and therefore the area occupied by the storage capacitor cannot be used as a display area thereby reducing the display luminance. However, it is desirable to have a large Cs to improve image quality. Therefore, a balance must be achieved between the display luminance and Cs size.